Sub miniature glow lamp and method of manufacture



F. H. RIXTON Aug. 28, 1956 SUB MINIATURE GLOW LAMP AND 'METHOD OF MANUFACTURE 2 Sheets-Sheet 1 Filed oct. 29, 1952 4 INVENTOR.

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F. H. RIXTON SUB MINIATURE GLOW LAMP AND METHOD OF' MANUFACTURE Filed 0G13. 29, 1953 2 Sheets-Sheet 2 Eff- INVENTOR. F. H. Fuffa/v small lamps are Patented Aug. 28, 1956 SUB WIATURE GLGW LAMP AND ME'IHD F MAN UFACTURE Frederick H. liixton, Livingston, N. J., assigner to West inghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application ctober 29, 1953, Serial No. 388,964 3 Claims. (Cl. 313-181) The present invention relates to discharge lamps and, more particularly, to glow discharge lamps for use as indicators and a method of manufacture.

With the development of more complex and` sensitive industrial machinery and inspection equipment and the design of automatic electrical appliances and devices, being applied in ever increasing numbers, firstly to indicate whether or not a device is properly connected in the circuit, secondly to show whether or not the circuit is alive; or thirdly, to give indication fof the operating sequence of automatic machinery the setting of a machine or the arrangement of the controls, or` any one of many other conditions that exist` with present day devices. .v

There are two basic types of lamps that can be used for such purposes-namely, the incandescent filament lamps and the less well known glow discharge or neon glow lamps. The small filament indicator lamp has a tungsten wire filament that produces visible light by incandescence and is generally of the vacuum type. These lamps are usually applied when both some ldegree of illumination and indication is required. On the other hand, glow lamps, in which the light is generated by al discharge of electricity through a gas, are especially satisfactory when t 2 In the manufacture of such a miniature glow lamp` of such small size it was found that the lamp volume was so small that very minute quantities of contaminants adonly visual indication or recording of data on film` is required.

Lamps for most industrial indicator applications are subject to rough service. In this field the glow lamp is unsurpassed because of its simple rugged construction. It is a small wattage light source that can be applied in conjunction with a small carbon type resistor at voltages as high as 450 to 6G() volts, or as low as 110` volts. Es sentially, these lamps consist of a side viewed glass bulb in which are sealed two rod-like vertical electrodes coated with an emission material.

Neon gas is used to fill the standard types. When energized the gas becomes ionized and current flows between the positive and negative electrodes, causing a characteristic orange-red glow to develop over the surface of the cathode (negative electrode). The lamps are often called negative glow lamps because only the negative electrode glows` at any one instant. of course, only the cathode glows. reversals are so rapid that both electrodes appear to glow together. This characteristic makes the glow lamp especially applicable for an inexpensive polarity tester.

In the design of digital recording device a plurality, for

On D. C. operation, T On A. C. the polarity example 5G, of these glow lamps may be mounted side by space within a camera housing adjacent a as the description thereof proceeds.

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versely affect the above mentioned desired characteristics of the glow lamp of my invention. For instance the melting of the glass exhaust tube during the tip-off (on exhaustlmay release sufiicient gaseous contaminants from the glass itself to be detrimental to the operating characteristic of the lamp. ln addition the space limitation of my` miniature glow lamp makes the incorporation of necessary parts, such as a getter impossible, unless novel and unique manufacturing assembly procedures are followed. In addition the bulb envelope, because of the space limitation, is so close to the discharge pathbetween the electrodes that striking voltages are quite high and it becomes a problem to achieve the above mentioned de- Sirable striking voltage, in the order of llOvolts D. C. Still further to achieve the very short ionization delay times in the order of 500 microseconds (and to avoid long and erratic ionization delay times) a continuous source of ions must be maintained within the miniature glow lamp.

Hence, it has been found advantageous according to my invention to provide a miniature glow discharge lamp having a maximum outside diameter of .055 and a maximum overall length of 1% for use in digital recording devices. In addition, the miniature glow discharge lamp of my invention has a striking voltage in the order of volts D. C. and a very short ionization delay time in the order of 500 micro-seconds. I have also found it advantageous to employ a novel cathode assembly having unique getter introducing means. Further I employ a radioactive material, as an ionization agent on my cathode assembly in addition to the emission material to aid in lowering the striking voltage and the ionization delay time to the desirable above specified limitation of 100` volts D. C.

Hence, it ing to my invention to` provide a method of manufacture within the manufactured lamps, and provides a novel mined quantities, t'

An additional object isa novel lamp, whereby minute `quantities of gaseous contaminants which adversely affect the` operating vchar,acteristics of mated.

A st ill further object is amethod of manufacture Jof my `miniature glow discharge lam herein a. novel method of introducing getter is employed.

the lamp may be` elmif Other objects of the present invention will become apj parent to those skilled in the art to Referring now to thedrawings wher of reference indicate similar pa Fig'. isa full scale side elevational viewbf ture glow discharge lamp of my invention.

Fig. 2 is an enlarged view similar to Fig. 1,

`ein like numeralsl rts throughout the several theprninia-l partially in vertical section, showing the cathode and anode assemblies of the lamp of Fig. 1.

Fig. 3 is a horizontal sectional view of the anode assembly of the lamp of Fig. 2 along the lines lll-III of Fig. 2 in the direction of the arrows.

Fig. 4 is a view similarV to Fig. 3 of the cathode assembly ofthe lamp of Fig. 2 along the lines lV-lV of Fig. 2 in the direction of the arrows.

Fig. 5 is a view similar to Figs. 3 and 4 of the gettering means in the cathode assembly of the lamp of Fig. 2 along the lines V-V of Fig. 2 in the direction of the arrows.

Fig. 6 is a vertical sectional view of the cathode assembly along the lines VI-VI of Fig. 2 in the direction of the arrows.

Fig. 7 is a side elevational view of the cathode assembly showing the sealing of the envelope to the cathode assembly.

Fig. 8 is a side elevational view showing the sealing of the lamp envelope to the anode assembly.

Fig. 9 is a side elevational view of the anode end of the lamp of Figs. 1, 2, 3 and 8 and an exhaust reservoir adapted for sealing to an exhaust manifold.

Referring now the drawings in detail and particularly to Fig. l the reference numeral 10 designates a miniature glow discharge lamp of my invention having a maximum diameter of .055" and a maximum overall length of 1%, a striking voltage in the order of 110 volts D. C. and a very short ionization delay time in the order of 500 microseconds.

The lamp 10, as shown particularly in Fig. 1, has a tubular vitreous envelope 12, an anode 14 and a cathode assembly 16 sealed to the opposite ends of said envelope 12.

Cathode assembly The cathode assembly 16 (Figs. l, 2, 6, 7 and 8) comprises essentially a rod-like cathode electrode 18 inserted in one end of a cathode tube 20. The cathode electrode 18 may suitably be a nickel wire approximately .025 in diameter and 4 mm. long. The cathode tube 20 appropriately may consist of a length of Kovar tubing approximately .030" to .035 in outside diameter and having a .005 wall thickness. It will be understood that the cathode electrode 13 is mounted suitably liush with one end of the cathode tube 20 and that the cathode tube 20 extends substantially beyond the lower end of the cathode electrode 18.

Approximately 1 to 2 mm. below the end of the cathode electrode 18, a pair of getter holes 22 are provided on opposite sides of the cathode tube 20 (Fig. 6).

A V-shaped self-positioning getter 24 is inserted into the cathode tube 20 and positioned therein between the cathode electrode 18 and the getter holes 22 so that the getter may vaporize through the getter holes 22 to the walls of the lamp envelope 12. The getter 24 may suitably comprise a V-shaped piece of iron or nickel clad barium getter wire to provide outwardly self-positioning ends for engagement with the inner side walls of cathode tube 20.

The lower end of the cathode tube 20 is then hermetically sealed, as by spot Welding, at a plurality of points, for example 3, inthe showing of Figs. 2 and 6, as at 26, 28 and 30. The cathode electrode 18 may be coated with emission material 32, which suitably may comprise a mixture of barium and strontium carbonate. The mixture of carbonates is later reduced by heating during the exhaust cycle to a mixture of barium and strontium oxide.

In addition an ionizing agent 34, such as a drop of radio active material (suitable an aqueous solution of either radium bromide, barium radium carbonate, meso thorium bromide or like material) is applied to the outside of the cathode tube 20 below the emission material 32. Radio active foil may also be employed as a substitute for the above mentioned radio active aqueous solutions. The ionizing agent 34 aids in lowering the 4 striking voltage and the ionization delay time of the lamp 10.

The cathode assembly 16 is then inserted and positioned in one end of the tubular envelope 12 which may comprise a suitable Kovar sealing glass tube approximately .055 in outside diameter and about 3M long. A vacuum type metal-to-glass seal (Fig. 7) is then made between the envelope 12 and the cathode tube 20, between the getter holes 22 in the cathode tube 20 and the spot welds at 26, 28 and 30. This seal may be made in any suitable manner, such as by rotating the envelope 12 and the cathode assembly 16 between the tires of a stationary burner 36 (Fig. 7) or by holding the envelope 12 and the cathode assemblies 16 stationary and rotating such a burner 36 about the area to be sealed to plasticize and collapse the lower end of the envelope 12 into vacuum tight engagement with the cathode tube 20.

Anode The anode 14 comprises essentially an anode tube, namely, a piece of Kovar tubing of the same size employed for the cathode tube 20. This anode 14 is positioned within the other end of the tubular envelope 12 so that the anode to cathode spacing is in the range of 0.5 to 1.0 mm. Prior to its insertion within the envelope 12, the anode 14 may be treated with a drop of radio active material if desired. The anode 14 is lthen sealed, as shown in Fig. 8, by means of a burner 42, in the same manner as the cathode assembly 16 was sealed to the other end of the envelope 12. The anode 14, a portion of which extends substantially beyond the seal, then serves as a combination anode and exhaust tube for the lamp 10. y

To provide a reservoir of till gas and a relatively large volume, which will minimize the total percentage of gaseous contamination evolved during the exhausting and the subsequent tipping-off of the lamp 10, an exhaust arm assembly 50 (Fig. 9) is sealed to `the upper end of the anode 14. This assembly 50 may suitably have a piece of glass tubing S1 approximately 1A in diameter and about 4" in length. The arm or tube 51 is provided with a reduced lower portion 52 to permit the satisfactory `sealing thereof to the upper end of the anode 14. In addition a constriction is provided in the upper end of the tube 51 at 54 to facilitate the eventual tip-off of the lamp 10 and the exhaust arm assembly 50 from an exhaust manifold (not shown). A getter support tube 56 may be positioned within the tube 50 for carrying additional getter material 58 thereon to aid in reducing lamp contamination during the exhaust cycle.

Method of exhaust After-Sealing the lamp 10 and the exhaust arm assembly 50 to an exhaust manifold (not shown) the system is evacuated by a suitable means (not shown), such as a vacuum pump. The entire assembly is then baked at an appropriate temperature to remove water vapor from the glass parts of the lamp 10 and the exhaust arm assembly 50. The anode 14 and the cathode assembly 16 are then induction heated to a suitable temperature to outgas the parts and to convert the emission material 32 from the carbonate to the oxide form.

The getter 24 within the cathode assembly 16 is then dashed by suitable means such as an induction coil through the getter holes 22 in the cathode tube 20 onto the wall of the envelope 12. To further reduce the danger of gas contamination of the lamp 10 at this stage of its exhaust, the getter 5S within the exhaust arm assembly 50 is also ashed onto the inner wall of the exhaust tube assembly 50.

An inert gaseous mixture of from 99.0 to 99.7% neon with the balance argon or some other inert gas or inert gaseous mixture (as determined by the application of the lamp) is then introduced within the lamp 10 and the exhaust arm assembly 50 to a pressure in the order of 120 mm. The exhaust arm assembly 50 and, of course, the lamp 10 are then sealed ot from the manifold (not shown) at the constriction 54 in the tube 51. The lamp 10 accompanied by the exhaust arm assembly 50 is then activated, seasoned and tested in the usual manner.

After activation, seasoning and testing the anode 14 is spot welded at a plurality of places in its upper end, for example 3, at 60, 62 and 64 to make a vacuum tight seal and is then cut, as by shears from the exhaust arm assembly 50 (Fig. 2). An anode pigtail lead 70 is aixed to the upper end of the anode 14 as by welding. A similar cathode pigtail 72 is, in like manner, applied to the lower end of the cathode tube 20 of the cathode assembly 16 to complete the lamp 10.

Although a preferred embodiment of my invention has been disclosed it will be understood that modifications may be made within the spirit and scope of the invention.

I claim:

l. A miniature glow discharge lamp for a digital recording device having a low striking voltage and a short ionization delay time comprising a vitreous envelope and an ionizable medium in said envelope, an anode sealed to one end of said envelope and a cathode assembly sealed to the other end of said envelope, said anode comprising a combination exhaust tube and electrode, said cathode assembly comprising a cathode tube and provided with getter outlet means and an hermetic seal below the getter outlet means, a rod-like cathode electrode within said cathode tube and a self-positioning getter within said cathode tube and beneath said cathode electrode.

2. A miniature glow discharge lamp for a digital recording device having a low striking voltage and a short ionization delay time comprising a vitreous envelope and an ionizable medium in said envelope, an anode sealed to one end of said envelope and a cathode assembly sealed to the other end of said envelope, said anode comprising a metallic combination exhaust tube and. electrode, said cathode assembly comprising a cathode tube treated with an ionizing agent and provided with getter outlet means and an hermetic seal below the getter outlet means, a rod-like cathode electrode Within said cathode tube and a self-positioning getter within said cathode tube and beueath said cathode electrode.

3. A miniature glow` discharge lamp for a digital recording device having a low striking voltage and a short ionization delay time comprising a vitreous envelope and an ionizable medium in said envelope, an anode sealed to one end of said envelope and a cathode assembly sealed to the other end of said envelope, said anode comprising a metallic combination exhaust tube and electrode, said cathode assembly comprising a cathode tube treated with an ionizing agent thereon and provided with getter outlet means and an hermetic seal at a plurality of points below the getter outlet means, a rod-like cathode electrode within said cathode tube and coated with emission material on one end, and a selfepositioning getter within said cathode tube and beneath said cathode electrode.

References Cited in the file of this; patent UNITED STATES PATENTS 1,618,767 Machlett Feb. 22, 1927 1,893,085 Johnson Ian. 3, 1933 2,492,619 Casellin Dec. 27, 1949 FOREIGN PATENTS 682,555 Great Britain Nov. l1, 1952 

